U.S. patent application number 15/296732 was filed with the patent office on 2017-04-27 for electrostatic latent image developing toner.
This patent application is currently assigned to KYOCERA Document Solutions Inc.. The applicant listed for this patent is KYOCERA Document Solutions Inc.. Invention is credited to Kazuki TSUCHIHASHI.
Application Number | 20170115583 15/296732 |
Document ID | / |
Family ID | 58558468 |
Filed Date | 2017-04-27 |
United States Patent
Application |
20170115583 |
Kind Code |
A1 |
TSUCHIHASHI; Kazuki |
April 27, 2017 |
ELECTROSTATIC LATENT IMAGE DEVELOPING TONER
Abstract
An electrostatic latent image developing toner contains a
plurality of toner particles each including a toner core and a
shell layer disposed over a surface of the toner core. The shell
layer has at least one first domain having a film shape and a
plurality of second domains each having a particle shape. The first
domain is formed substantially from a non-crosslinked resin. The
second domains are formed substantially from a crosslinked resin.
The crosslinked resin has a glass transition point 45.degree. C. or
more greater than the non-crosslinked resin. The first domain has
an average height from the surface of the toner core of at least 10
nm and less than 50 nm. The second domains have an average height
from the surface of the toner core of at least 50 nm and no greater
than 100 nm.
Inventors: |
TSUCHIHASHI; Kazuki;
(Osaka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KYOCERA Document Solutions Inc. |
Osaka |
|
JP |
|
|
Assignee: |
KYOCERA Document Solutions
Inc.
Osaka
JP
|
Family ID: |
58558468 |
Appl. No.: |
15/296732 |
Filed: |
October 18, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03G 9/09371 20130101;
G03G 9/08711 20130101; G03G 9/0819 20130101; G03G 9/08755 20130101;
G03G 9/08728 20130101; G03G 9/09364 20130101; G03G 9/0825 20130101;
G03G 9/09335 20130101; G03G 9/09392 20130101; G03G 9/09321
20130101; G03G 9/08733 20130101 |
International
Class: |
G03G 9/08 20060101
G03G009/08; G03G 9/087 20060101 G03G009/087; G03G 9/093 20060101
G03G009/093 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 21, 2015 |
JP |
2015-207125 |
Claims
1. An electrostatic latent image developing toner comprising a
plurality of toner particles each including a core and a shell
layer disposed over a surface of the core, wherein the shell layer
has at least one first domain having a film shape and a plurality
of second domains each having a particle shape, the first domain is
formed substantially from a non-crosslinked resin, the second
domains are formed substantially from a crosslinked resin, the
crosslinked resin has a glass transition point 45.degree. C. or
more greater than the non-crosslinked resin, the first domain has
an average height from the surface of the core of at least 10 nm
and less than 50 nm, and the second domains have an average height
from the surface of the core of at least 50 nm and no greater than
100 nm.
2. The electrostatic latent image developing toner according to
claim 1, wherein a ratio of a region of the core covered with the
first domain relative to an entire surface region of the core is at
least 40% and no greater than 80%.
3. The electrostatic latent image developing toner according to
claim 2, wherein the first domain and the second domains are
stacked in order of the first domain and the second domains from a
side close to the core, and a ratio of a region of the core covered
with either or both of the first domain and the second domains
relative to the entire surface region of the core is at least 70%
and no greater than 99%.
4. The electrostatic latent image developing toner according to
claim 1, wherein the first and second domains have the same
polarity.
5. The electrostatic latent image developing toner according to
claim 1, wherein the shell layer contains a cationic
surfactant.
6. The electrostatic latent image developing toner according to
claim 1, wherein the first domain and the second domains are
stacked in order of the first domain and the second domains from a
side close to the core.
7. The electrostatic latent image developing toner according to
claim 6, wherein the shell layer has a first region constituted
only by the first domain, a second region constituted only by some
of the second domains, and a third region in which the first domain
and some of the second domains are superposed on one another, and
an area of the second region is larger than that of the third
region.
8. The electrostatic latent image developing toner according to
claim 1, wherein a difference obtained by subtracting the average
height of the first domain from the average height of the second
domains is at least 30 nm and no greater than 90 nm.
9. The electrostatic latent image developing toner according to
claim 1, wherein the core contains a polyester resin, the
crosslinked resin is a crosslinked acrylic acid-based resin, and
the non-crosslinked resin is a non-crosslinked styrene-acrylic
acid-based resin.
10. The electrostatic latent image developing toner according to
claim 9, wherein the crosslinked acrylic acid-based resin is a
polymer of (meth)acrylic acid alkyl ester having at an ester
portion thereof an alkyl group having a carbon number of at least 1
and no greater than 3 and di(meth)acrylic acid ester of alkylene
glycol having an alkylene group having a carbon number of at least
1 and no greater than 4.
11. The electrostatic latent image developing toner according to
claim 9, wherein the non-crosslinked styrene-acrylic acid-based
resin has one or more repeating units each derived from a
styrene-based monomer, one or more repeating units each derived
from (meth)acrylic acid alkyl ester, and one or more repeating
units each having an alcoholic hydroxyl group, and one of the one
or more repeating units each derived from a styrene-based monomer
has a highest molar ratio among the repeating units that the
non-crosslinked styrene-acrylic acid-based resin has.
12. The electrostatic latent image developing toner according to
claim 1, wherein the core has a glass transition point lower than
the non-crosslinked resin.
Description
INCORPORATION BY REFERENCE
[0001] The present application claims priority under 35 U.S.C.
.sctn.119 to Japanese Patent Application No. 2015-207125, filed on
Oct. 21, 2015. The contents of this application are incorporated
herein by reference in their entirety.
BACKGROUND
[0002] The present disclosure relates to an electrostatic latent
image developing toner.
[0003] Toner particles contained in a capsule toner each have a
core and a shell layer (capsule layer) disposed over a surface of
the core. In an example of a capsule toner producing method, cores
(toner cores) are mixed with resin particulates having two
different glass transition points (glass transition temperatures)
to form shell layers on the surfaces of the respective cores.
SUMMARY
[0004] An electrostatic latent image developing toner according to
the present disclosure includes a plurality of toner particles each
including a core and a shell layer disposed over a surface of the
core. The shell layer has at least one first domain having a film
shape and a plurality of second domains each having a particle
shape. The first domain is formed substantially from a
non-crosslinked resin. The second domains are formed substantially
from a crosslinked resin. The crosslinked resin has a glass
transition point 45.degree. C. or more greater than the
non-crosslinked resin. The first domain has an average height from
the surface of the core of at least 10 nm and less than 50 nm. The
second domains have an average height from the surface of the core
of at least 50 nm and no greater than 100 nm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a cross sectional view illustrating an example of
a toner particle (specifically, a toner mother particle) contained
in an electrostatic latent image developing toner according to an
embodiment of the present disclosure.
[0006] FIG. 2 illustrates in an enlarged scaled a part of a surface
of the toner mother particle illustrated in FIG. 1.
[0007] FIG. 3 is a photograph of a surface of a toner mother
particle taken for the toner according to the embodiment of the
present disclosure using a scanning probe microscope (SPM).
[0008] FIG. 4 is a photograph of a section of a toner mother
particle (specifically, a section of a shell layer) taken for the
toner according to the embodiment of the present disclosure using a
transmission electron microscope (TEM).
DETAILED DESCRIPTION
[0009] The following explains an embodiment of the present
disclosure in detail. Unless otherwise stated, evaluation results
(for example, values indicating shape and physical properties) for
a powder (specific examples include toner cores, toner mother
particles, external additive, and toner) are number averages of
values measured for a suitable number of particles.
[0010] Unless otherwise stated, a number average particle diameter
of the powder is a number average value of equivalent circular
diameters of primary particles (diameters of circles having the
same areas as projected areas of the respective particles) measured
using a microscope. A measured value of a volume median diameter
(D.sub.50) of the powder is a value measured using "Coulter Counter
Multisizer 3" manufactured by Beckman Coulter, Inc. unless
otherwise stated. Respective measured values of an acid value and a
hydroxyl value are values measured in accordance with Japan
Industrial Standard (JIS) K0070-1992 unless otherwise stated. A
number average molecular weight (Mn) and a mass average molecular
weight (Mw) are values measured by gel permeation chromatography
unless otherwise stated.
[0011] In the present description, the term "-based" may be
appended to the name of a chemical compound in order to form a
generic name encompassing both the chemical compound itself and
derivatives thereof. When the term "-based" is appended to the name
of a chemical compound used in the name of a polymer, the term
indicates that a repeating unit of the polymer originates from the
chemical compound or a derivative thereof. In the present
description, the term "(meth)acryl" is used as a generic term for
both acryl and methacryl.
[0012] A toner according to the present embodiment can be favorably
used as for example a positively chargeable toner for development
of an electrostatic latent image. The toner according to the
present embodiment is a powder containing a plurality of toner
particles (particles each having structure described later in
detail). The toner may be used as a one-component developer.
Alternatively, the toner may be mixed with a carrier using a mixer
(specific example include a ball mill) to prepare a two-component
developer. A ferrite carrier is preferably used as the carrier in
order to form a high-quality image. It is preferable to use
magnetic carrier particles each including a carrier core and a
resin layer that covers the carrier core in order to form
high-quality images for a long period of time. Carrier cores may be
formed from a magnetic material (for example, a ferromagnetic
material such as ferrite) or a resin in which magnetic particles
are dispersed in order to impart magnetism to the carrier
particles. Alternatively, magnetic particles may be dispersed in
resin layers that cover respective carrier cores. The amount of the
toner in a two-component developer is preferably at least 5 parts
by mass and no greater than 15 parts by mass relative to 100 parts
by mass of the carrier, and more preferably at least 8 parts by
mass and no greater than 12 parts by mass, in order to form a
high-quality image. Note that the positively chargeable toner
contained in the two-component developer is positively charged by
friction with the carrier.
[0013] The toner particles contained in the toner according to the
present embodiment each include a core (also referred to below as a
toner core) and a shell layer (capsule layer) disposed over a
surface of the toner core. The toner core contains a binder resin.
The toner core may optionally contain an internal additive (for
example, a colorant, a releasing agent, a charge control agent, and
a magnetic powder). An external additive may be attached to a
surface of the shell layer (or a surface region of the toner core
that is not covered with the shell layer). Note that the external
additive may be omitted in a situation in which such additives are
not necessary. Hereinafter, toner particles that are yet to be
subjected to addition of an external additive are referred to as
toner mother particles. A material for forming the shell layers is
referred to as a shell material.
[0014] The toner according to the present embodiment can be used
for for example image formation using an electrophotographic
apparatus (image forming apparatus). Following describes an example
of an image forming method using an electrophotographic
apparatus.
[0015] First, an image forming section (a charger and an exposure
device) of the electrophotographic apparatus forms an electrostatic
latent image on a photosensitive member (for example, a surface
layer portion of a photosensitive drum) based on image data. Next,
the formed electrostatic latent image is developed using a
developer containing a toner. In a development process, toner (for
example, toner charged by friction with the carrier or a blade) on
a development sleeve (for example, a surface layer portion of a
development roller in the developing device) disposed in the
vicinity of the photosensitive member is attached to the
electrostatic latent image to form a toner image on the
photosensitive member. In a subsequent transfer process, the toner
image on the photosensitive member is transferred to an
intermediate transfer member (for example, a transfer belt), and
the toner image on the intermediate transfer member is further
transferred to a recording medium (for example, paper). Thereafter,
a fixing device (fixing method: nip fixing using a heating roller
and a pressure roller) applies heat and pressure to the toner to
fix the toner to the recording medium. As a result, an image is
formed on the recording medium. A full-color image can be obtained
by superimposing toner images formed using different colors, such
as black, yellow, magenta, and cyan. A belt fixing method may be
adopted as a fixing method.
[0016] The toner according to the present embodiment is an
electrostatic latent image developing toner having the following
structure (also referred to below as basic structure).
[0017] (Basic Structure of Toner)
[0018] The electrostatic latent image developing toner contains a
plurality of toner particles each including a toner core and a
shell layer. The shell layer has at least one first domain having a
film shape and second domains each having a particle shape. The
first domain is formed substantially from a non-crosslinked resin.
The second domains are formed substantially from a crosslinked
resin. The crosslinked resin has a glass transition point (Tg)
45.degree. C. or more greater than the non-crosslinked resin. The
first domain has an average height (hereinafter referred to as a
first shell thickness) from the surface of the toner core of at
least 10 nm and less than 50 nm. The second domains have an average
height (hereinafter referred to as a second shell thickness) from
the surface of the toner core of at least 50 nm and no greater than
100 nm. The first domain may each have a film shape with or without
granular appearance. A method for measuring the first and second
shell thicknesses is the same as that described in Examples
described later or an alternative method thereof.
[0019] The toner having the above basic structure is excellent in
both high-temperature preservability and fixability. Operation and
advantages of the above basic structure will be described
below.
[0020] For example, high-temperature preservability of the toner
can be improved by covering each of the toner cores with a resin
film. Resin particles can be used as a material used for forming
the resin film. The resin film can be formed by dissolving (or
deforming) resin particles and hardening them into a film shape.
When the resin film is formed on the surface of each toner core
using non-crosslinked resin particles having a low glass transition
point (Tg), a wide range of the surface of each toner core can be
covered with a thin resin film (film of a non-crosslinked resin
having a low Tg). However, the non-crosslinked resin film formed as
above tends to involve significant variation in thickness.
Irregularity in film thickness as above is expected to be caused
due to agglomeration of the resin particles. When an area ratio of
a region of the surface region of the toner core where the toner
core is exposed from the resin film (region not covered with the
resin film) is large, high-temperature preservability of the toner
tends to be impaired. By contrast, when the thickness of the resin
film is increased so that the surface of the toner core is covered
entirely with the resin film, low-temperature fixability of the
toner tends to be impaired.
[0021] The inventor has found that uniform shell layers can be
formed (and sufficient high-temperature preservability of the toner
can be ensured as a result) by covering incompletely (at a low
coverage) the surfaces of the toner cores with a non-crosslinked
resin film and filling gaps among the films with crosslinked resin
particles. The toner having the above basic structure contains the
toner cores each including a shell layer having the film-shaped
first domain and the particle-shaped second domains. The first
domain is formed substantially from a non-crosslinked resin. The
second domains are formed substantially from a crosslinked resin.
The crosslinked resin has a glass transition point (Tg) 45.degree.
C. or more greater than the non-crosslinked resin. Covering the
toner cores with the first domain (low-Tg non-crosslinked resin
film) and the second domains (high-Tg crosslinked resin particles)
can improve both high-temperature preservability and
low-temperature fixability of the toner. The presence of the second
domains in a region of a surface region of the toner core where the
toner core is exposed from the first domain can reduce the first
shell thickness comparatively thin to ensure low-temperature
fixability of the toner and improve high-temperature preservability
of the toner.
[0022] In the above basic structure, Tg of the crosslinked resin is
45.degree. C. or more greater than that of the non-crosslinked
resin. The second domains, which have a comparatively high Tg, are
expected to contribute to improvement in heat resistance of the
toner particles. In order to form high-quality shell layers,
difference obtained by subtracting Tg of the non-crosslinked resin
from Tg of the crosslinked resin (=(Tg of crosslinked resin)-(Tg of
non-crosslinked resin)) is preferably at least 45.degree. C. and no
greater than 80.degree. C. The respective glass transition points
(Tg) of the crosslinked resin and the non-crosslinked resin can be
adjusted by for example changing species or amounts (blend ratio)
of components (monomers) of the respective resins.
[0023] In the above basic structure, the first shell thickness is
at least 10 nm and less than 50 nm and the second shell thickness
is at least 50 nm and no greater than 100 nm. The inventor has
found that formation of shell layers such as above can improve both
high-temperature preservability and low-temperature fixability of
the toner (see Tables 1-3 indicated later). The second domains each
have a comparatively large particle diameter (second shell
thickness) relative to the first shell thickness. In the above
configuration, the second domains are expected to function as
spacers among the toner particles to inhibit agglomeration of the
toner particles. In order to enhance functionality of the second
domains as the spacers, a difference obtained by subtracting the
first shell thickness from the second shell thickness (also
referred to below as a shell height difference) is preferably at
least 30 nm and no greater than 90 nm. The shell height difference
is represented by an equation "shell height difference=(second
shell thickness)-(first shell thickness)".
[0024] In order to improve both high-temperature preservability and
low-temperature fixability of the toner, a first domain and second
domains constitute a stacked structure of the first domain and the
second domains in stated order from a side close to the toner core.
For example, when the low-Tg non-crosslinked resin (or a precursor
thereof) is attached to the surfaces of the toner cores and then
the high-Tg crosslinked resin particles are attached to the
surfaces of the toner cores in shell layer formation, a stacked
structure as above can be formed. In a situation in which the first
and second domains are formed at the same time, the low-Tg
non-crosslinked resin tends to be attached to the toner cores prior
to the high-Tg crosslinked resin. However, the non-crosslinked
resin films are expected to be partly formed on the crosslinked
resin particles. In a configuration in which too many regions where
the crosslinked resin particles and the non-crosslinked resin film
are stacked in the stated order are present in the surface region
of the toner core, low-temperature fixability of the toner is
expected to be impaired.
[0025] The first and second domains preferably have the same
polarity in order to improve both high-temperature preservability
and low-temperature fixability of the toner. Electrical repulsion
between the first and second domains tends to cause the second
domains to be disposed in gaps in the first domain. The first and
second domains preferably have an opposite polarity (for example,
cationicity) to the polarity (for example anionicity) of the toner
cores in order to increase bonding strength between the toner cores
and the shell layers.
[0026] The glass transition point of the toner cores is preferably
lower than that of the non-crosslinked resin of the first domain in
the above basic structure in order to improve low-temperature
fixability of the toner.
[0027] Following describes an example of structure of the toner
according to the present embodiment with reference to FIGS. 1 and
2. FIG. 1 illustrates an example of a configuration of a toner
particle (specifically, a toner mother particle) contained in the
toner according to the present embodiment. FIG. 2 is an enlarged
view of a part of the toner mother particle illustrated in FIG.
1.
[0028] A toner mother particle 10 illustrated in FIG. 1 includes a
toner core 11 and a shell layer 12 disposed over a surface of the
toner core 11. The shell layer 12 is formed substantially from
resin. The shell layer 12 covers a surface of the toner core
11.
[0029] As illustrated in FIG. 2, the shell layer 12 of the toner
mother particle 10 includes a film-shaped first domain 12a and
particle-shaped second domains 12b. In the example illustrated in
FIG. 2, first and second domains 12a and 12b constitute a stacked
structure in order of the first domain 12a and the second domain
12b from a side close to the toner core 11. That is, the first
domain 12a is located more closely to the toner core 11 than the
second domains 12b. The first domain 12a is each attached to the
surface of the toner core 11. Some second domains 12b are attached
to the surface of the first domain 12a. By contrast, some second
domains 12b may be attached to the surface of the toner core 11 in
a region of a surface region of the toner core 11 where no first
domain 12a is present.
[0030] The surface of the toner core 11 is partly covered with the
shell layer 12. A region of the surface region of the toner core 11
covered with either or both of the first and second domains 12a and
12b corresponds to covered regions (regions each covered with the
shell layer 12). A region of the shell layer 12 (specifically, a
region in a direction perpendicular to a thickness direction of the
shell layer 12) can be divided into the following three regions
(first to third regions).
[0031] The first region is a region of the shell layer 12 that is
constituted only by the first domain 12a directly covering the
surface of the toner core 11 (region in which no second domain 12b
is present on the first domain 12a).
[0032] There are regions in which the second domains 12b are
present and regions in which no second domain 12b is present among
regions of the surface of the toner core 1 that are exposed from
the first domain 12a. The second region is a region of the shell
layer 12 that is constituted only by second domains 12b directly
covering the surface of the toner core 11.
[0033] In a surface region of each first domain 12a, there are a
region in which a second domain 12b is present and a region in
which no second domain 12b is present. The presence of a second
domain 12b on a first domain 12a covering the surface of the toner
core 11 means that the surface of the toner core 11 is covered with
both the first and second domains 12a and 12b. The first domain 12a
located below the second domain 12b (on the side close to the toner
core 11) directly covers the surface of the toner core 11, while
the second domain 12b located on the first domain 12a (on a side
away from the toner core 11) indirectly covers the surface of the
toner core 11. The third region is a region of the shell layer 12
in which the first domain 12a and second domains 12b that cover the
surface of the toner core 11 are superposed on one on the
other.
[0034] The shell layer 12 has regions (first regions) each
constituted only by a first domain 12a, a region (second region)
constituted only by second domains 12b, and a region (third region)
in which the first domain 12a and second domains 12b are superposed
on one another. The area of the second region is preferably larger
than the area of the third region in order to improve both
high-temperature preservability and low-temperature fixability of
the toner. In a configuration in which the area of the third region
is too large, it is expected to be difficult to fix toner at low
temperature. In a configuration in which the area of the second
region is too small, the second domains 12b are expected to
insufficiently exhibit a role for improving high-temperature
preservability of the toner.
[0035] Referring to FIG. 2, a first height D1 indicates a height of
a first domain 12a from the surface of the toner core 11. A second
height D2 indicates a height of a second domain 12b from the
surface of the toner core 11. The first height D1 is a height of a
first domain 12a measured in a first region of the shell layer 12.
The second height D2 is a height of a second domain 12b measured in
a second region of the shell layer 12. The first and second heights
D1 and D2 each correspond to a thickness of the shell layer 12. The
first shell thickness in the above basic structure corresponds to
an arithmetic mean value of first heights D1 (for example, an
arithmetic mean of ten or more measured values). The second shell
thickness in the above basic structure corresponds to an arithmetic
mean value of second heights D2 (for example, an arithmetic mean of
ten or more measured values).
[0036] The first and second domains 12a and 12b can be confirmed by
observing the surface of a toner mother particle 10 using a
scanning probe microscope (SPM). FIG. 3 is a photograph of the
surface of the toner mother particle 10 taken for the toner
according to the present embodiment using a SPM. For example, a
resin film (a film-shaped first domain 12a) can be confirmed in a
region R1 in FIG. 3. Also, a resin particle (a particle-shaped
second domain 12b) can be confirmed in a region R2 in FIG. 3.
[0037] The first and second shell thicknesses each can be confirmed
by observing a cross section of the toner mother particle 10 using
a transmission electron microscope (TEM). FIG. 4 is a photograph of
a section of the toner mother particle 10 (specifically, section of
the shell layer 12) taken for the toner according to the present
embodiment using a TEM. It can be confirmed from the photograph of
FIG. 4 that the shell layer 12 has projections and recesses
(specifically, projections and recesses corresponding to first and
second domains 12a and 12b).
[0038] A rate (also referred to below as a first coverage) of a
surface region of the toner core covered with the first domain
(also referred to below as a first covered region) relative to an
entire surface region of the toner core is preferably at least 40%
and no greater than 80% in order to improve both high-temperature
preservability and low-temperature fixability of the toner. The
first covered region includes a surface region of the toner core
covered with only a first domain and a surface region of the toner
core covered with both first and second domains. The first coverage
(unit: %) is represented by an equation "first
coverage=100.times.(area of first covered region)/(area of entire
surface region of toner core)". In a configuration in which the
first domain is too thick, the first coverage is too high. As such,
low-temperature fixability of the toner is expected to be impaired.
In a configuration in which the first coverage is too low, many
second domains are necessary for ensuring high-temperature
preservability of the toner. As such, it is expected to be
difficult to improve both high-temperature preservability and
low-temperature fixability of the toner.
[0039] A rate (also referred to below as a second coverage) of a
region (also referred to below as a second covered region) of the
toner core covered with either or both of the first domain and the
second domains relative to the entire surface region of the toner
core is preferably at least 70% and no greater than 99% in order to
improve both high-temperature preservability and low-temperature
fixability of the toner. The second covered region includes a
surface region of the toner core covered with only a first domain,
a surface region of the toner core covered with only a second
domain, and a surface region of the toner core covered with both
first and second domains. The second coverage (unit: %) is
represented by an equation "second coverage=100.times.(area of
second covered region)/(area of entire surface region of toner
core)".
[0040] It is particularly preferable in order to improve both
high-temperature preservability and low-temperature fixability of
the toner that: first and second domains constitute a stacked
structure of the shell layer in which the first and second domains
are stacked in the order of the first domain and the second domain
from the side close to the toner core; the first coverage is at
least 40% and no greater than 80%; and the second coverage is at
least 70% and no greater than 99%.
[0041] The toner preferably has a volume median diameter (D.sub.50)
of at least 1 .mu.m and less than 10 .mu.m in order to improve both
high-temperature preservability and low-temperature fixability of
the toner.
[0042] Hereinafter, the cores (a binder resin and an internal
additive), the shell layers, and the external additive will be
described in order. Non-essential components (for example, an
internal additive or an external additive) may be omitted in
accordance with the intended use of the toner.
[0043] <Preferable Thermoplastic Resin>
[0044] Examples of thermoplastic resins that can be preferably used
for forming the toner particles (particularly, the toner cores and
the shell layers) include styrene-based resins, acrylic acid-based
resins (specific examples include an acrylic acid ester polymer and
a methacrylic acid ester polymer), olefin-based resins (specific
examples include a polyethylene resin and a polypropylene resin),
vinyl chloride resins, polyvinyl alcohol, vinyl ether resins,
N-vinyl resins, polyester resins, polyamide resins, and urethane
resins. A copolymer of any of the resins listed above, that is, a
copolymer of any of the resins listed above into which an optional
repeating unit is included (specific examples include a
styrene-acrylic acid-based resin and a styrene-butadiene-based
resin) is also preferably used as a thermoplastic resin forming the
toner particles.
[0045] A styrene-acrylic acid-based resin is a copolymer of at
least one styrene-based monomer and at least one acrylic acid-based
monomer. In a situation in which a styrene-acrylic acid-based resin
is synthesized, any of styrene-based monomers and any of acrylic
acid-based monomers that are listed below can for example be used
favorably. Use of an acrylic acid-based monomer having a carboxyl
group can result in inclusion of the carboxyl group into a
styrene-acrylic acid-based resin. Use of a monomer having a
hydroxyl group (specific examples include p-hydroxystyrene,
m-hydroxystyrene, and (meth)acrylic acid hydroxyalkyl ester) can
result in inclusion of the hydroxyl group into a styrene-acrylic
acid-based resin. The acid value of a resultant styrene-acrylic
acid-based resin can be adjusted through appropriate adjustment of
the amount of the acrylic acid-based monomer to use. The hydroxyl
value of the resultant styrene-acrylic acid-based resin can be
adjusted through appropriate adjustment of the amount of the
hydroxyl group-containing monomer to use.
[0046] Examples of preferable styrene-based monomers include
styrene, .alpha.-methylstyrene, p-hydroxystyrene, m-hydroxystyrene,
vinyltoluene, .alpha.-chlorostyrene, o-chlorostyrene,
m-chlorostyrene, p-chlorostyrene, and p-ethylstyrene.
[0047] Examples of preferable acrylic acid-based monomers include
(meth)acrylic acids, (meth)acrylic acid alkyl esters, and
(meth)acrylic acid hydroxyalkyl esters. Examples of preferable
(meth)acrylic acid alkyl esters include (meth)methyl acrylate,
(meth)ethyl acrylate, (meth)n-propyl acrylate, (meth)iso-propyl
acrylate, (meth)n-butyl acrylate, (meth)iso-butyl acrylate, and
(meth)2-ethylhexyl acrylate. Examples of preferable (meth)acrylic
acid hydroxyalkyl esters include (meth)2-hydroxyethyl acrylate,
(meth)3-hydroxypropyl acrylate, (meth)2-hydroxypropyl acrylate, and
(meth)4-hydroxybutyl acrylate.
[0048] A polyester resin can be yielded by condensation
polymerization of at least one polyhydric alcohol and at least one
polybasic carboxylic acid. Examples of alcohols that can be used
for synthesis of a polyester resin include dihydric alcohols
(specific examples include diols and bisphenols) and tri- or
higher-hydric alcohols listed below. Examples of carboxylic acids
that can be preferably used for synthesis of a polyester resin
include dibasic carboxylic acids and tri- or higher-basic
carboxylic acids listed below. The acid value and the hydroxyl
value of a polyester resin can be adjusted through appropriate
adjustment of the respective amounts of an alcohol and an
carboxylic acid to use during synthesis of the polyester resin.
Increasing the molecular weight of a polyester resin tends to
decrease the acid value and the hydroxyl value of the polyester
resin.
[0049] Examples of preferable diols include ethylene glycol,
diethylene glycol, triethylene glycol, 1,2-propanediol,
1,3-propanediol, 1,4-butanediol, neopentyl glycol,
2-butene-1,4-diol, 1,5-pentanediol, 1,6-hexanediol,
1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol,
polypropylene glycol, and polytetramethylene glycol.
[0050] Examples of preferable bisphenols include bisphenol A,
hydrogenated bisphenol A, bisphenol A ethylene oxide adducts, and
bisphenol A propylene oxide adducts.
[0051] Examples of preferable tri- or higher-hydric alcohols
include sorbitol, 1,2,3,6-hexanetetraol, 1,4-sorbitan,
pentaerythritol, dipentaerythritol, tripentaerythritol,
1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol,
2-methylpropanetriol, 2-methyl-1,2,4-butanetriol,
trimethylolethane, trimethylolpropane, and
1,3,5-trihydroxymethylbenzene.
[0052] Examples of preferable dibasic carboxylic acids include
maleic acid, fumaric acid, citraconic acid, itaconic acid,
glutaconic acid, phthalic acid, isophthalic acid, terephthalic
acid, cyclohexanedicarboxylic acid, adipic acid, sebacic acid,
azelaic acid, malonic acid, succinic acid, alkyl succinic acids
(specific examples include n-butylsuccinic acid, isobutylsuccinic
acid, n-octylsuccinic acid, n-dodecylsuccinic acid, and
isododecylsuccinic acid), and alkenylsuccinic acids (specific
examples include n-butenylsuccinic acid, isobutenylsuccinic acid,
n-octenylsuccinic acid, n-dodecenylsuccinic acid, and
isododecenylsuccinic acid).
[0053] Examples of preferable tri- or higher-basic carboxylic acids
include 1,2,4-benzenetricarboxylic acid (trimellitic acid),
2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic
acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic
acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane,
1,2,4-cyclohexanetricarboxylic acid,
tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic
acid, pyromellitic acid, and EMPOL trimer acid.
[0054] [Toner Core]
[0055] (Binder Resin)
[0056] The binder resin is typically a main component (for example,
at least 85% by mass) of the toner cores. Properties of the binder
resin are therefore expected to have great influence on an overall
property of the toner cores. The toner cores have a strong tendency
to be anionic when the binder resin has a group such as an ester
group, a hydroxyl group, an ether group, an acid group, or a methyl
group. By contrast, the toner cores have a strong tendency to be
cationic when the binder resin has a group such as an amino group
or an amide group. In order that the binder resin is strongly
anionic, the hydroxyl value and the acid value of the binder resin
each are preferably no less than 10 mgKOH/g.
[0057] The binder resin preferably has one or more groups selected
from the group consisting of an ester group, a hydroxyl group, an
ether group, an acid group, and a methyl group with either or both
of a hydroxyl group and a carboxyl group being more preferable. The
binder resin having such a functional group can readily react with
the shell material to form chemical bonds. Such chemical bonding
causes strong bonding between the toner cores and the shell layers.
Furthermore, the binder resin preferably has an activated
hydrogen-containing functional group in molecules thereof.
[0058] The toner cores preferably contain a crystalline polyester
resin in order to improve fixability of the toner in high speed
fixing. The toner cores preferably have a glass transition point
(Tg) of at least 20.degree. C. and no greater than 55.degree. C. in
order to improve fixability of the toner in high speed fixing. The
toner core preferably have a softening point (Tm) of no greater
than 100.degree. C. in order to improve fixability of the toner in
high speed fixing. Note that a method for measuring Tg and Tm is
the same as that described in Examples described later or
alternative methods thereof. Changing the species or amount (blend
ratio) of the components (monomers) of the resin can result in
adjustment of either or both of Tg and Tm of the resin. A
combination of plural types of resins can also result in adjustment
of either or both of Tg and Tm of the binder resin.
[0059] The binder resin of the toner cores is preferably a
thermoplastic resin (specific examples include "examples of
preferable thermoplastic resins" listed above). A styrene-acrylic
acid-based resin or a polyester resin is preferably used as the
binder resin in order to improve dispersibility of a colorant in
the toner cores, chargeability of the toner, and fixability of the
toner to a recording medium.
[0060] In a configuration in which a styrene-acrylic acid-based
resin is used as the binder resin of the toner cores, the
styrene-acrylic acid-based resin preferably has a number average
molecular weight (Mn) of at least 2,000 and no greater than 3,000
in order to improve strength of the toner cores and fixability of
the toner. The styrene-acrylic acid-based resin preferably has a
molecular weight distribution (ratio Mw/Mn of mass average
molecular weight (Mw) relative to number average molecular weight
(Mn)) of at least 10 and no greater than 20.
[0061] In a configuration in which a polyester resin is used as the
binder resin of the toner cores, the polyester resin preferably has
a number average molecular weight (Mn) of at least 1,000 and no
greater than 2,000 in order to improve strength of the toner cores
and fixability of the toner. The polyester resin preferably has a
molecular weight distribution (ratio Mw/Mn of mass average
molecular weight (Mw) relative to number average molecular weight
(Mn)) of at least 9 and no greater than 21.
[0062] (Colorant)
[0063] The toner cores may each contain a colorant. The colorant
can be a known pigment or dye that matches the color of the toner.
The amount of the colorant is preferably at least 1 part by mass
and no greater than 20 parts by mass relative to 100 parts by mass
of the binder resin in order to form a high-quality image using the
toner.
[0064] The toner cores may contain a black colorant. Carbon black
can for example be used as a black colorant. Alternatively, a
colorant that is adjusted to a black color using a yellow colorant,
a magenta colorant, and a cyan colorant can for example be used as
a black colorant.
[0065] The toner cores may contain a non-black colorant such as a
yellow colorant, a magenta colorant, or a cyan colorant.
[0066] One or more compounds selected from the group consisting of
condensed azo compounds, isoindolinone compounds, anthraquinone
compounds, azo metal complexes, methine compounds, and arylamide
compounds can be used for example as a yellow colorant. Specific
examples of yellow colorants that can be preferably used include C.
I. Pigment Yellow (3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95,
97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155, 168,
174, 175, 176, 180, 181, 191, and 194), Naphthol Yellow S, Hansa
Yellow Q and C. I. Vat Yellow.
[0067] One or more compounds selected from the group consisting of
condensed azo compounds, diketopyrrolopyrrole compounds,
anthraquinone compounds, quinacridone compounds, basic dye lake
compounds, naphthol compounds, benzimidazolone compounds,
thioindigo compounds, and perylene compounds can be used for
example as a magenta colorant. Specific examples of magenta
colorants that can be preferably used include C. I. Pigment Red
(for example, 2, 3, 5, 6, 7, 19, 23, 48:2, 48:3, 48:4, 57:1, 81:1,
122, 144, 146, 150, 166, 169, 177, 184, 185, 202, 206, 220, 221,
and 254).
[0068] One or more compounds selected from the group consisting of
copper phthalocyanine compounds, anthraquinone compounds, and basic
dye lake compounds can be used for example as a cyan colorant.
Examples of cyan colorants that can be preferably used include C.
I. Pigment Blue (1, 7, 15, 15:1, 15:2, 15:3, 15:4, 60, 62, and 66),
Phthalocyanine Blue, C. I. Vat Blue, and C. I. Acid Blue.
[0069] (Releasing Agent)
[0070] The toner cores may each contain a releasing agent. The
releasing agent is for example used in order to improve fixability
of the toner or resistance of the toner to being offset. The toner
cores are preferably produced using an anionic wax in order to
increase anionic strength of the toner cores. The amount of the
releasing agent is preferably at least 1 part by mass and no
greater than 30 parts by mass relative to 100 parts by mass of the
binder resin in order to improve fixability or offset resistance of
the toner.
[0071] Examples of releasing agents that can be preferably used
include: aliphatic hydrocarbon waxes such as low molecular weight
polyethylene, low molecular weight polypropylene, polyolefin
copolymer, polyolefin wax, microcrystalline wax, paraffin wax, and
Fischer-Tropsch wax; oxides of aliphatic hydrocarbon waxes such as
polyethylene oxide wax and block copolymer of polyethylene oxide
wax; plant waxes such as candelilla wax, carnauba wax, Japan wax,
jojoba wax, and rice wax; animal waxes such as beeswax, lanolin,
and spermaceti; mineral waxes such as ozokerite, ceresin, and
petrolatum; waxes having a fatty acid ester as a main component
such as montanic acid ester wax and castor wax; and waxes in which
a part or all of a fatty acid ester has been deoxidized such as
deoxidized carnauba wax. One of the releasing agents listed above
may be used, or a combination of two or more of the releasing
agents listed above may be used.
[0072] A compatibilizer may be added to the toner cores in order to
improve compatibility between the binder resin and the releasing
agent.
[0073] (Charge Control Agent)
[0074] The toner cores may each contain a charge control agent. The
charge control agent is for example used in order to improve charge
stability or a charge rise characteristic of the toner. The charge
rise characteristic of the toner is an indicator as to whether the
toner can be charged to a specific charge level in a short period
of time.
[0075] Containment of a negatively chargeable charge control agent
(specific examples include an organic metal complex and a chelate
compound) in the toner cores can increase anionic strength of the
toner cores. By contrast, containment of a positively chargeable
charge control agent (specific examples include pyridine,
nigrosine, and quaternary ammonium salt) in the toner cores can
increase cationic strength of the toner core. However, the toner
cores need not to contain a charge control agent in a configuration
in which sufficient chargeability of the toner can be ensured.
[0076] (Magnetic Powder)
[0077] The toner cores may each contain a magnetic powder. Examples
of materials of the magnetic powder that can be preferably used
include ferromagnetic metals (specific examples include iron,
cobalt, nickel, and an alloy containing one or more of the listed
metals), ferromagnetic metal oxides (specific examples include
ferrite, magnetite, and chromium dioxide), and materials subjected
to ferromagnetization (specific examples include carbon materials
to which ferromagnetism is imparted through thermal treatment). One
type of the magnetic powders listed above may be used, or a
combination of two or more types of the magnetic powders listed
above may be used.
[0078] The magnetic powder is preferably subjected to surface
treatment in order to inhibit elution of metal ions (e.g., iron
ions) from the magnetic powder. In a situation in which the shell
layers are formed over the surfaces of the toner cores under acidic
conditions, elution of metal ions to the surfaces of the toner
cores may cause the toner cores to adhere to one another more
readily. It is expected that inhibition of elution of metal ions
from the magnetic powder can inhibit toner cores from adhering to
one another.
[0079] [Shell Layer]
[0080] The toner according to the present embodiment has the above
basic structure. The shell layers each have the first domain having
a film-shape and the second domains each having a particle shape.
The first domain is formed substantially from the non-crosslinked
resin. The second domains are formed substantially from the
crosslinked resin.
[0081] The first and second domains each are preferably formed
substantially from a polymer (resin) of monomers containing at
least one vinyl compound. A polymer of monomers containing at least
one vinyl compound has a repeating unit derived from the vinyl
compound. When domains are formed through polymerization of a vinyl
compound having a functional group according to a desired function
to be imparted to the toner, the function can be imparted to the
domains easily and accurately. Note that the vinyl compound is a
compound having a vinyl group (CH.sub.2.dbd.CH--) or a group
substituted by hydrogen in a vinyl group (specific examples include
ethylene, propylene, butadiene, vinyl chloride, acrylic acid,
methyl acrylate, methacrylic acid, methyl methacrylate,
acrylonitrile, and styrene). The vinyl compound can be a
macromolecule (resin) through addition polymerization by carbon
double bonding "C.dbd.C" included in the vinyl group or the
like.
[0082] The non-crosslinked resin forming the first domain is
preferably a non-crosslinked thermoplastic resin (specific examples
include the "preferable thermoplastic resins" listed above) and
particularly preferably a non-crosslinked styrene-acrylic
acid-based resin in order to improve both high-temperature
preservability and low-temperature fixability of the toner.
[0083] Examples of non-crosslinked resins that can preferably form
the first domain include a polymer (also referred to below as a
specific non-crosslinked resin) of at least one styrene-based
monomer, at least one (meth)acrylic acid alkyl ester, and at least
one (meth)acrylic acid hydroxyalkyl ester. A polymer such as above
has at least one repeating unit derived from the styrene-based
monomer, at least one repeating unit derived from (meth)acrylic
acid alkyl ester, and at least one repeating unit derived from
(meth)acrylic acid hydroxyalkyl ester.
[0084] Examples of preferable repeating units derived from a
styrene-based monomer that the specific non-crosslinked resin
forming the first domain has include a repeating unit represented
by the following formula (1).
##STR00001##
[0085] In the formula (1), R.sup.11 to R.sup.15 each represent,
independently of one another, a hydrogen atom, a halogen atom, a
hydroxyl group, an optionally substituted alkyl group, an
optionally substituted alkoxy group, or an optionally substituted
aryl group. Further, R.sup.16 and R.sup.17 each represent,
independently of one another, a hydrogen atom, a halogen atom, or
an optionally substituted alkyl group. Preferably, R.sup.11 to
R.sup.15 each represent, independently of one another, a hydrogen
atom, a halogen atom, an alkyl group having a carbon number of at
least 1 and no greater than 4, an alkoxy group having a carbon
number of at least 1 and no greater than 4, or an alkoxyalkyl group
having a carbon number (specifically, a total carbon number of
alkoxy and alkyl) of at least 2 and no greater than 6. Preferably,
R.sup.16 and R.sup.17 each represent, independently of one another,
a hydrogen atom or a methyl group. A combination of R.sup.7
representing a hydrogen atom and R.sup.16 representing a hydrogen
atom or a methyl group is particularly preferable. Note that
R.sup.11 to R.sup.17 each represent a hydrogen atom in a repeating
unit derived from styrene. Further, R.sup.13 represents a chloro
group (Cl--) and R.sup.11, R.sup.12, and R.sup.14 to R.sup.17 each
represent a hydrogen atom in a repeating unit derived from
4-chlorostyrene. In a repeating unit derived from
2-(ethoxymethyl)styrene, R.sup.11 represents an ethoxymethyl group
(C.sub.2HsOCH.sub.2--) and R.sup.12 to R.sup.17 each represent a
hydrogen atom.
[0086] A repeating unit having the highest molar ratio among
repeating units that the resin forming the first domain has is
preferably a repeating unit derived from a styrene-based monomer in
order that the shell layers have sufficiently strong hydrophobicity
and appropriate strength.
[0087] Examples of preferable repeating units derived from
(meth)acrylic acid hydroxyalkyl ester that the specific
non-crosslinked resin forming the first domain has include a
repeating unit represented by the following formula (2).
##STR00002##
[0088] In the formula (2), R.sup.21 and R.sup.22 each represent,
independently of one another, a hydrogen atom, a halogen atom, or
an optionally substituted alkyl group. Further, R.sup.3 represents
an optionally substituted alkylene group. Preferably, R.sup.21 and
R.sup.22 each represent, independently of one another, a hydrogen
atom or a methyl group. A combination of R.sup.21 representing a
hydrogen atom and R.sup.22 representing a hydrogen atom or a methyl
group is particularly preferable. Preferably, R.sup.3 represents an
alkylene group having a carbon number of at least 1 and no greater
than 6 with an alkylene group having a carbon number of at least 1
and no greater than 4 being more preferable. In a repeating unit
derived from 2-hydroxyethyl methacrylate (HEMA): R.sup.21
represents a hydrogen atom; R.sup.22 represents a methyl group; and
R.sup.3 represents an ethylene group (--(CH.sub.2).sub.2--).
[0089] Preferably, the specific non-crosslinked resin forming the
first domain does not have a repeating unit having at least one of
an acid group, a hydroxyl group, and salts thereof except a
repeating unit having an alcoholic hydroxyl group in order to
inhibit separation of the shell layers and sufficiently inhibit
adsorption of moisture in the air to the surfaces of the shell
layers.
[0090] The crosslinked resin forming the second domains is
preferably a thermoplastic resin having cross-linking structure
(specific examples include the "preferable thermoplastic resins"
listed above) and more preferably a crosslinked acrylic acid-based
resin in order to improve both high-temperature preservability and
low-temperature fixability of the toner. Di(meth)acrylic acid ester
of alkylene glycol (specific examples include ethylene glycol
dimethacrylate) is preferable as a cross-linking agent for
introducing cross-linking structure to the acrylic acid-based
resin.
[0091] A crosslinked resin cross-linked with di(meth)acrylic acid
ester of alkylene glycol has a repeating unit derived from
di(meth)acrylic acid ester of alkylene glycol. Examples of
preferable repeating units derived from di(meth)acrylic acid ester
of alkylene glycol that the crosslinked resin forming the second
domains has include a repeating unit represented by the following
formula (3).
##STR00003##
[0092] In the formula (3): R.sup.41 represents a hydrogen atom or a
methyl group; R.sup.42 represents a hydrogen atom or a methyl
group; and R.sup.5 represents an optionally substituted alkylene
group. Preferably, R.sup.5 represents an alkylene group having a
carbon number of at least 1 and no greater than 8 with an alkylene
group having a carbon number of at least 1 and no greater than 4
being more preferable. Note that R.sup.41 and R.sup.42 each
represent a methyl group and R.sup.5 represents an ethylene group
(--(CH.sub.2).sub.2--) in a repeating unit derived from ethylene
glycol dimethacrylate.
[0093] In a preferable example of the toner, the toner cores
contain a polyester resin and each have the first domain formed
substantially from the non-crosslinked styrene-acrylic acid-based
resin and the second domains made substantially of the crosslinked
acrylic acid-based resin. A toner such as above tends to be
excellent in all of high-temperature preservability,
low-temperature fixability, and chargeability. Further, the first
and second domains tend to be readily charged positively. As such,
electrical repulsion among the first and second domains tends to
cause the second domains to be disposed in gaps in the first
domain. The toner cores tend to be readily charged negatively. As
such, the toner cores tend to bond to the shell layers
strongly.
[0094] It is preferable that the non-crosslinked styrene-acrylic
acid-based resin forming the first domain has one or more repeating
units each derived from a styrene-based monomer, one or more
repeating units each derived from (meth)acrylic acid alkyl ester,
and one or more repeating units each having an alcoholic hydroxyl
group and a repeating unit having the highest molar ratio among the
repeating units that the resin forming the first domain has is a
repeating unit derived from a styrene-based monomer. Examples of
preferable styrene-based monomers include styrene, alkyl styrene
having an alkyl group having a carbon number of at least 1 and no
greater than 4 (specific examples include methylstyrene and
butylstyrene), alkoxy styrene having an alkoxy group having a
carbon number of at least 1 and no greater than 4 (specific
examples include methoxystyrene), alkoxy alkyl styrene having an
alkoxy alkyl group having a carbon number (specifically, a total
carbon number of alkoxy and alkyl) of at least 2 and no greater
than 6 (specific examples include 2-(ethoxymethyl)styrene),
bromostyrene, and chlorostyrene. Examples of preferable
(meth)acrylic acid alkyl esters include (meth)methyl acrylate,
(meth)ethyl acrylate, (meth)n-propyl acrylate, (meth)iso-propyl
acrylate, (meth)n-butyl acrylate, and (meth)iso-butyl acrylate. A
preferable monomer having an alcoholic hydroxyl group (monomer for
including a repeating unit having an alcoholic hydroxyl group into
a resin) is 2-hydroxy alkyl ester (meth)acrylate. Examples of
preferable 2-hydroxy alkyl ester (meth)acrylates include
2-hydroxyethyl acrylate (HEA), 2-hydroxy propyl acrylate (HPA),
2-hydroxyethyl methacrylate (HEMA), and 2-hydroxy propyl
methacrylate.
[0095] A particularly preferable crosslinked acrylic acid-based
resin forming the second domains is a polymer of (meth)acrylic acid
alkyl ester having at an ester portion thereof an alkyl group
having a carbon number of at least 1 and no greater than 3
(specific examples include methyl methacrylate) and di(meth)acrylic
acid ester of alkylene glycol having an alkylene group having a
carbon number of at least 1 and no greater than 4 (specific
examples include ethylene glycol dimethacrylate and dimethacrylate
butanediol).
[0096] The shell layers preferably contain a cationic surfactant in
order to increase strength of positive chargeability of the toner.
By leaving a cationic surfactant used for forming the shell layers
rather than thorough removal thereof, the shell layers can remain
containing the cationic surfactant. In a situation for example in
which a suspension (shell material) of resin particles is prepared
using a cationic surfactant, the cationic surfactant is attached to
the surfaces of the resin particles in a suspension when the
cationic surfactant is left in the suspension. Formation of shell
layers using a suspension as above can result in the shell layers
in which the cationic surfactant is attached to the surfaces of
either or both of the first and second domains. Examples of
cationic surfactants that can be contained in the shell layers
include amine salts (specific examples include an acetic acid salt
of primary amine) and quaternary ammonium salts (specific examples
include an alkyl trimethyl ammonium salt, a dialkyl dimethyl
ammonium salt, an alkyl benzyl dimethyl ammonium salt, an
acryloyloxyalkyl trimethyl ammonium salt, a methacryloyloxy alkyl
trimethyl ammonium salt, and benzethonium chloride).
[0097] [External Additive]
[0098] An external additive may be attached to the surfaces of the
toner mother particles. When the toner mother particles (powder)
and the external additive (powder of inorganic particles) are
stirred together, parts (bottom parts) of the external additive
particles are embedded in surface layer portions of the toner
mother particles such that the external additive particles are
attached to the surfaces of the toner mother particles by a
physical power (physical bond). The external additive is used for
example for improving fluidity or handling property of the toner.
The amount of the external additive is preferably at least 0.5
parts by mass and no greater than 10 parts by mass relative to 100
parts by mass of the toner mother particles in order to improve
fluidity or handling property of the toner. In order to improve
fluidity or handling property of the toner, the external additive
preferably has a particle diameter of at least 0.01 .mu.m and no
greater than 1.0 .mu.m.
[0099] Inorganic particles are preferable and silica particles or
particles of metal oxides (specific example include alumina,
titanium oxide, magnesium oxide, zinc oxide, strontium titanate,
and barium titanate) are particularly preferable as the external
additive particles. One type of external additive particles may be
used, or a combination of two or more types of external additive
particles may be used.
[0100] [Toner Production Method]
[0101] Following describes an example of a method for producing the
toner according to the present embodiment that has the above basic
structure. First of all, toner cores are prepared. Subsequently,
the toner cores and a shell material are added to a liquid. It is
preferable to dissolve or disperse the shell material in the liquid
by for example stirring the liquid containing the shell material in
order to form a uniform shell layer. Subsequently, the shell
material and the toner cores are bonded together by for example
keeping the liquid at high temperature to form shell layers
(hardened resin layers) on the surfaces of the toner cores. In
order to inhibit dissolution or elution of toner core components
(particularly, a binder resin and a releasing agent) during
formation of the shell layers, the formation of the shell layers is
preferably carried out in an aqueous medium. The aqueous medium is
a medium of which main component is water (specific examples
include pure water and a liquid mixture of water and a polar
medium). The aqueous medium may function as a solvent. A solute may
be dissolved in the aqueous medium. The aqueous medium may function
as a dispersion medium. A dispersoid may be dispersed in the
aqueous medium. Examples of polar mediums in the aqueous medium
that can be used include alcohols (specific examples include
methanol and ethanol). The boiling point of the aqueous medium is
approximately 100.degree. C.
[0102] Following describes a method for producing the toner
according to the present embodiment by referring to a more specific
example.
[0103] (Preparation of Toner Cores)
[0104] In order to easily obtain preferable toner cores, the toner
cores are preferably produced according to an aggregation method or
a pulverization method and more preferably according to the
pulverization method.
[0105] An example of the pulverization method will be described
below. First, a binder resin and an internal additive (for example,
at least one of a colorant, a releasing agent, a charge control
agent, and a magnetic powder) are mixed together. Subsequently, the
resultant mixture is melt-knead. The resultant melt-knead substance
is pulverized and classified. Through the above, toner cores having
a desired particle diameter can be obtained.
[0106] An example of the aggregation method will be described
below. First, binder resin particles, releasing agent particles,
and colorant particles are aggregated until the particles each have
a desired particle diameter in an aqueous medium containing the
respective particles. As a result, aggregated particles of the
binder resin, the releasing agent, and the colorant are formed.
Subsequently, the resultant aggregated particles are heated for
coalescence of the components contained in the aggregated
particles. As a result, a dispersion of the toner cores is
obtained. Thereafter, unnecessary substances (a surfactant and the
like) are removed from the dispersion of the toner cores to obtain
toner cores.
[0107] (Formation of Shell Layer)
[0108] An aqueous medium (for example, ion exchanged water) is
prepared as the liquid to which the toner cores and the shell
material are added. Subsequently, the pH of the aqueous medium is
adjusted to a specific pH (for example, at least 3 and no greater
than 5) using for example hydrochloric acid. Subsequently, toner
cores and a suspension of a non-crosslinked resin (liquid
containing non-crosslinked resin particles) are added to the
aqueous medium of which pH has been adjusted (for example, acidic
aqueous medium).
[0109] The toner cores and the shell material may be added to the
aqueous medium at room temperature or the aqueous medium of which
temperature is adjusted (kept) at a specific temperature. An
appropriate amount of the shell material to add can be calculated
based on the specific surface area of the toner cores.
[0110] The non-crosslinked resin particles are attached to the
surfaces of the toner cores in the liquid. Preferably, the toner
cores are highly dispersed in the liquid containing the
non-crosslinked resin particles in order to uniformly attach the
non-crosslinked resin particles to the surfaces of the toner cores.
In order to highly disperse the toner cores in the liquid, the
liquid may contain a surfactant or be stirred using a high-power
stirrer (for example, "Hivis Disper Mix" manufactured by PRIMIX
Corporation). Examples of surfactants that can be used include
sulfate ester salts, sulfonic acid salts, phosphate ester salts,
and soap.
[0111] Subsequently, the temperature of the liquid containing the
toner cores and the non-crosslinked resin particles is increased to
a first retention temperature (preferably, a temperature satisfying
"(Tg of non-crosslinked resin)-5.degree. C..ltoreq.(first retention
temperature).ltoreq.(Tg of non-crosslinked resin)+20.degree. C.)"
at a specific speed (for example at least 0.1.degree. C./min. and
no greater than 3.degree. C./min.) while the liquid is stirred
(first temperature increasing treatment). Alternatively, the
temperature of the liquid may be kept at the first retention
temperature for a specific time period (for example, at least one
minute and no greater than 60 minutes) while the liquid is stirred
after the first temperature increasing treatment (after the
temperature of the liquid reaches the first retention temperature).
The non-crosslinked resin particles are expected to be dissolved
during the first temperature increasing treatment (during the time
when the temperature of the liquid is increased to the first
retention temperature) or after the first temperature increasing
treatment (during the time when the temperature of the liquid is
kept at the first retention temperature). Adjustment of the first
retention temperature and Tg of the non-crosslinked resin can
result in adjustment of a dissolved state of the non-crosslinked
resin particles. For example, once the resin particles are
completely dissolved, a film having no granular appearance can be
formed.
[0112] Subsequently, a suspension of a crosslinked resin (liquid
containing crosslinked resin particles) is added to the liquid. The
temperature of the liquid is increased to a second retention
temperature (preferably, a temperature satisfying "(Tg of
non-crosslinked resin)-5.degree. C..ltoreq.(second retention
temperature).ltoreq.(Tg of crosslinked resin)-20.degree. C.)" at a
specific speed (for example, at least 0.1.degree. C./min. and no
greater than 3.degree. C./min.) while the liquid is stirred (second
temperature increasing treatment). Note that the second retention
temperature may be equal to the first retention temperature. In a
method in which the second retention temperature is equal to the
first retention temperature, the second temperature increasing
treatment may be omitted.
[0113] Subsequently, the temperature of the liquid containing the
crosslinked resin particles is kept at the second retention
temperature for a specific time period (for example, at least 30
minute and no greater than four hours) while the liquid is stirred.
The shell layers are formed on the surfaces of the toner cores
during the temperature increasing treatment (first or second
temperature increasing treatment) or during the time when the
temperature of the liquid is kept at high temperature (the first or
second retention temperature). Specifically, it is expected that a
non-crosslinked resin film (first domain) is formed on the surfaces
of the toner cores and crosslinked resin particles (second domains)
are attached to gaps among the non-crosslinked resin films.
[0114] After the shell layers are formed as above, a dispersion of
toner mother particles is cooled to for example normal temperature
(approximately 25.degree. C.). The dispersion of the toner mother
particles is then filtered using for example a Buchner funnel.
Filtration of the dispersion of the toner mother particles
separates the toner mother particles from the liquid (solid-liquid
separation), thereby collecting a wet cake of the toner mother
particles. Next, the resultant wet cake of the toner mother
particles is washed. The toner mother particles that have been
washed are then dried. Thereafter, as necessary, the toner mother
particles may be mixed with an external additive using a mixer (for
example, an FM mixer manufactured by Nippon Coke & Engineering
Co., Ltd.) to attach the external additive to the surfaces of the
toner mother particles. In a situation in which a spray dryer is
used in the drying process, the drying process and the external
additive process can be carried out at the same time by spraying a
dispersion of an external additive (for example, silica particles)
to the toner mother particles. Through the above, a toner
containing multiple toner particles is produced.
[0115] Note that processes and order of the method for producing
the toner described above may be changed freely in accordance with
desired structure, characteristics, and the like of the toner. The
toner may be sifted after external addition. Also, non-essential
processes may alternatively be omitted. For example, in a method in
which a commercially available product can be used directly as a
material, use of the commercially available product can omit the
process of preparing the material. In a method in which reaction
for forming the shell layers progresses favorably even without pH
adjustment of the liquid, the process of pH adjustment may be
omitted. In a method in which no external additive is necessary,
the external addition process may be omitted. In a method in which
an external additive is not attached to the surfaces of the toner
mother particles (i.e., a method in which the external addition
process is omitted), the toner mother particles are equivalent to
the toner particles. A prepolymer may be used instead of the
monomer as a material for resin synthesis (for example, a toner
core material or a shell material), depending on necessity. In
order to yield a specific compound, a salt, ester, hydrate, or
anhydride of the compound may be used as a raw material.
Preferably, a large number of the toner particles are formed at the
same time in order to produce the toner efficiently. The toner
particles produced at the same time are thought to have
substantially the same configuration.
EXAMPLES
[0116] Following describes examples of the present disclosure.
Table 1 indicates toners T-1 to T-15 according to examples and
comparative examples (each are an electrostatic latent image
developing toner). Table 2 indicates suspensions A-1 to A-5 and B-1
to B-6 used for manufacturing any of the toners T-1 to T-15. The
terms "1st" and "2nd" in the item of "height (unit: nm)" in Table 1
mean the first and second shell thicknesses, respectively. The term
"particle diameter" in Table 2 means a number average value of
equivalent circular diameters of primary particles measured using a
scanning electron microscope (SEM).
TABLE-US-00001 TABLE 1 Tg difference First shell Second shell
between shell material material materials Height Amount Amount (2nd
- 1st) [nm] First coverage Toner Type [mL] Type [mL] [.degree. C.]
1st 2nd [%] T-1 A-1 15 B-3 20 62 (=130 - 68) 16 79 69 T-2 A-2 B-3
57 (=130 - 73) 20 83 58 T-3 A-3 B-3 48 (=130 - 82) 44 83 43 T-4 A-2
B-2 49 (=122 - 73) 22 68 71 T-5 A-1 B-1 46 (=114 - 68) 13 56 77 T-6
A-2 B-4 52 (=125 - 73) 20 95 65 T-7 A-2 10 B-5 61 (=134 - 73) 20 97
38 T-8 A-4 15 B-2 57 (=122 - 65) 12 76 82 T-9 A-1 15 A-3 15 14 (=82
- 68) -- -- 84 T-10 A-3 15 B-2 20 40 (=122 - 82) 41 69 60 T-11 A-2
B-1 41 (=114 - 73) 23 56 63 T-12 A-4 15 B-1 20 49 (=114 - 65) 9 56
88 T-13 A-5 B-3 46 (=130 - 84) 51 85 51 T-14 A-2 B-5 61 (=134 - 73)
20 101 65 T-15 A-1 B-6 37 (=105 - 68) 15 48 78
TABLE-US-00002 TABLE 2 Cross- Tg Particle diameter Dispersion
linking [.degree. C.] [nm] A-1 Absent 68 53 A-2 73 55 A-3 82 52 A-4
65 53 A-5 84 56 B-1 Present 114 84 B-2 122 84 B-3 130 90 B-4 125
114 B-5 134 109 B-6 105 77
[0117] Following describes methods for producing the respective
toners T-1 to T-15, evaluation methods, and evaluation results in
order. In evaluations in which errors may occur, an evaluation
value was calculated by calculating the arithmetic mean of an
appropriate number of measured values in order to ensure that any
errors were sufficiently small. Respective methods for measuring Tg
(glass transition point), Mp (melting point), and Tm (softening
point) are those described below unless otherwise stated.
[0118] <Methods for Measuring Tg and Mp>
[0119] A differential scanning calorimeter ("DSC-6220" manufactured
by Seiko Instruments Inc.) was used as a measuring device. Tg and
Mp of a sample (for example, a resin) was obtained through
measurement of a heat absorption curve of the sample using the
measuring device. Specifically, 15 mg of a sample (for example, a
resin) was put on an aluminum pan (aluminum container) and the
aluminum pan was set on a measurement section of the measuring
device. An empty aluminum pan was additionally used as a reference.
In measurement of the heat absorption curve, the temperature of the
measurement section was increased from a measurement starting
temperature of 10.degree. C. to 150.degree. C. at a rate of
10.degree. C./min. (RUN1). Thereafter, the temperature of the
measurement section was dropped from 150.degree. C. to 10.degree.
C. at a rate of 10.degree. C./min. Subsequently, the temperature of
the measurement section was re-increased from 10.degree. C. to
150.degree. C. at a rate of 10.degree. C./min. (RUN2). Performance
of RUN2 resulted in plot of a heat absorption curve (vertical axis:
heat flow (DSC signals), horizontal axis: temperature) of the
sample. Mp and Tg of the sample were read from the heat absorption
curve that was plotted. The temperature of a maximum peak derived
from heat of fusion on the heat absorption curve corresponds to Mp
(melting point) of the sample. Further, a temperature at a point of
change (intersection between an extrapolation line of a base line
and an extrapolation line of a fall line) in the specific heat on
the heat absorption curve corresponds to Tg (glass transition
point) of the sample.
[0120] <Tm Measuring Method>
[0121] A sample (for example, a resin) was placed in a capillary
rheometer ("CFT-500D" manufactured by Shimadzu Corporation), and
melt-flow of 1 cm.sup.3 of the sample was caused using a die
diameter of 1 mm, a plunger load of 20 kg/cm.sup.2, and a heating
rate of 6.degree. C./min. in order to plot an S-shaped curve
(horizontal axis: temperature, vertical axis: stroke) of the
sample. Then, Tm of the sample was read from the S-shaped curve
that was plotted. Tm (softening point) of the sample is a
temperature on the S-shaped curve corresponding to a stroke value
of (S.sub.1+S.sub.2)/2 where S.sub.1 represents a maximum value of
the stroke and S.sub.2 represents a base-line stroke value at
low-temperature.
[0122] For each of samples (toners T-1 to T-15), the first and
second shell thicknesses were measured using a scanning probe
microscope (SPM) by the following method and the first coverage of
the toner cores was measured using a transmission electron
microscope (TEM).
[0123] <Method for Measuring First and Second Shell
Thicknesses>
[0124] A scanning probe station ("NanoNaviReal" manufactured by
Hitachi High-Tech Science Corporation) equipped with a scanning
probe microscope (SPM) ("multifunctional unit AFM5200S"
manufactured by Hitachi High-Tech Science Corporation) was used as
a measuring device. Prior to measurement, average toner particles
were selected as a measurement target from among toner particles
included in a sample (toner) using a scanning electron microscope
(SEM) ("JSM-6700F" manufactured by JEOL Ltd.). The toner particles
were each directly set on the measurement table without being cut,
and a contour image of the toner particle was taken under the
following measurement conditions. A field of view of the measuring
device was set so that a first region (region constituted only by a
film-shape domain) and a second region (region constituted only by
a particle-shaped domain) of a shell layer were included in a
measurement range.
[0125] (SPM Measurement Conditions) [0126] Measurement prove:
low-spring constant silicon cantilever ("OMCL-AC240TS-C3"
manufactured by Olympus Corporation), spring constant: 2 N/m,
resonance frequency: 70 kHz, coating material for back reflection:
aluminum). [0127] Measurement mode: sampling intelligent
scan-dynamic force mode (SIS-DFM). [0128] Measurement range (per
one field of view): 1 .mu.m.times.1 .mu.m. [0129] Resolution (X
data/Y data): 256/256.
[0130] A contour image (image showing a surface contour) of the
toner particle was taken while a distance between the prove and the
toner particle was controlled so that the amplitude of the
vibrating cantilever (tip end: prove) was constant in a state in
which the cantilever is caused to resonate in the measurement mode
(SIS-DFM). The taken contour image was subjected to primary
inclination correction, and the respective heights of two types of
domains (films-shaped domains and particle-shaped domains) included
in the shell layer from the surface of the toner core were
measured. Five film-shaped domains were arbitrarily selected in the
first regions in the toner particle while the field of view was
changed, and the respective heights (first height D1 illustrated in
FIG. 2) of the selected five film-shaped domains were measured.
Furthermore, five particle-shaped domains were arbitrarily selected
in the second region while the field of view was changed and the
respective heights (second height D2 illustrated in FIG. 2) of the
selected five particle-shaped domains were measured. Five first
heights D1 and five second heights D2 were measured for each of ten
toner particles contained in the sample (toner). An arithmetic mean
of the measured values of the measured 50 first heights D1 and an
arithmetic mean of the measured values of the measured 50 second
heights D2 were defined as evaluation values (first and second
shell thicknesses) of the sample (toner).
[0131] <Method for Measuring First Coverage>
[0132] A sample (toner) was embedded in a visible photocurable
resin ("ARONIX (registered Japanese trademark) D-800" manufactured
by Toagosei Co., Ltd.) to yield a hardened material. Thereafter,
the yielded hardened material was cut at a cutting rate of 0.3
mm/sec. using a ultrathin piece forming knife ("Sumi Knife
(registered Japanese trademark)" manufactured by Sumitomo Electric
Industries, Ltd., a diamond knife having a blade width of 2 mm and
a blade tip angle of 45.degree.) and a ultramicrotome ("EM UC6"
manufactured by Leica Microsystems) to form a thin piece having a
thickness of 150 nm. The resultant thin piece was set on a copper
mesh and exposed to vapor of an aqueous solution of ruthenium
tetroxide for ten minutes for ruthenium dyeing. Subsequently, a
section of the dyed sample piece was taken using a transmission
electron microscope (TEM) ("JSM-6700F" manufactured by JEOL Ltd.).
The taken TEM image was analyzed using image analysis software
("WinROOF" manufactured by Mitani Corporation). A ratio of the
total length of regions covered with film-shaped domains relative
to the surface region (a contour line indicating an outer
circumference) of the toner core was measured in the taken TEM
image (sectional image of the toner particle). Specifically, the
first coverage was calculated based on an equation "first
coverage=100.times.(total length of regions covered with
film-shaped domains)/(circumferential length of toner core)". The
first coverage of the toner core was measured for each of ten toner
particles contained in the sample (toner). An arithmetic mean of
the calculated ten measured values was used as an evaluation value
(first coverage) of the sample (toner).
[0133] [Methods for Producing Toners T-1 to T-15]
[0134] (Synthesis of Crystalline Polyester Resin)
[0135] A 10-L four-necked flask equipped with a thermometer
(thermocouple), a dewatering conduit, a nitrogen inlet tube, and a
stirrer was charged with 2,643 g of 1,6-hexanediol, 864 g of
1,4-butanediol, and 2,945 g of succinic acid. Subsequently, the
flask contents were heated to 160.degree. C. to dissolve the
charged materials. Then, a liquid mixture of styrene and the like
(liquid mixture of 1,831 g of styrene, 161 g of acrylic acid, and
110 g of dicumyl peroxide) was dripped into the flask over one hour
using a dripping funnel. The flask contents were stirred at a
temperature of 170.degree. C. for one hour for reaction to
polymerize styrene and acrylic acid in the flask. Thereafter,
unreacted styrene and unreacted acrylic acid in the flask were
removed by keeping the flask contents in a reduced-pressure
atmosphere (pressure: 8.3 kPa) for one hour. Subsequently, 40 g of
tin(II) 2-ethylhexanoate and 3 g of gallic acid were added to the
flask. The flask contents were increased in temperature for
reaction at a temperature of 210.degree. C. for eight hours.
Subsequently, the flask contents were caused to react for one hour
in a reduced-pressure atmosphere (pressure: 8.3 kPa) at a
temperature of 210.degree. C. As a result, a crystalline polyester
resin having Tm of 92.degree. C., Mp of 96.degree. C., and a
crystallinity index of 0.95 was yielded. Note that the
crystallinity index of a resin corresponds to a rate (=Tm/Mp) of
the softening point (Tm) of the resin relative to the melting point
(Mp) of the resin.
[0136] (Synthesis of Non-Crystalline Polyester Resin A)
[0137] A 10-L four-necked flask equipped with a thermometer
(thermocouple), a dewatering conduit, a nitrogen inlet tube, and a
stirrer was charged with 370 g of a bisphenol A propylene oxide
adduct, 3,059 g of a bisphenol A ethylene oxide adduct, 1,194 g of
terephthalic acid, 286 g of fumaric acid, 10 g of tin(II)
2-ethylhexanoate, and 2 g of gallic acid. Subsequently, the flask
contents were caused to react in a nitrogen atmosphere at a
temperature of 230.degree. C. until the reaction rate became at
least 90% by mass. The reaction rate was calculated based on an
equation "reaction rate=100.times.(actual amount of reaction
product water)/(theoretical amount of reaction product water)". The
flask contents were then caused to react in a reduced-pressure
atmosphere (pressure: 8.3 kPa) until Tm of a reaction product
(resin) became a specific temperature (89.degree. C.). As a result,
a non-crystalline polyester resin A was yielded that had a Tm of
89.degree. C. and a Tg of 50.degree. C.
[0138] (Synthesis of Non-Crystalline Polyester Resin B)
[0139] A non-crystalline polyester resin B was synthesized
according to the same method as for the non-crystalline polyester
resin A in all aspects other than that 1,286 g of the bisphenol A
propylene oxide adduct, 2,218 g of the bisphenol A ethylene oxide
adduct, and 1,603 g of terephthalic acid were used instead of 370 g
of the bisphenol A propylene oxide adduct, 3,059 g of the bisphenol
A ethylene oxide adduct, 1,194 g of terephthalic acid, and 286 g of
fumaric acid. The non-crystalline polyester resin B had a Tm of
111.degree. C. and a Tg of 69.degree. C.
[0140] (Synthesis of Non-Crystalline Polyester Resin C)
[0141] A 10-L four-necked flask equipped with a thermometer
(thermocouple), a dewatering conduit, a nitrogen inlet tube, and a
stirrer was charged with 4,907 g of a bisphenol A propylene oxide
adduct, 1,942 g of a bisphenol A ethylene oxide adduct, 757 g of
fumaric acid, 2,078 g of dodecylsuccinic acid anhydride, 30 g of
tin(II) 2-ethylhexanoate, and 2 g of gallic acid. Subsequently, the
flask contents were caused to react in a nitrogen atmosphere at a
temperature of 230.degree. C. until the reaction rate represented
by the above equation became at least 90% by mass. The flask
contents were then caused to react for one hour in a
reduced-pressure atmosphere (pressure: 8.3 kPa). Subsequently, 548
g of trimellitic anhydride was added to the flask and the flask
contents were caused to react in a reduced-pressure atmosphere
(pressure: 8.3 kPa) at a temperature of 220.degree. C. until the Tm
of a reaction product (resin) became a specific temperature
(127.degree. C.). As a result, a non-crystalline polyester resin C
was yielded that had a Tm of 127.degree. C. and a Tg of 51.degree.
C.
[0142] (Preparation of Suspension A-1)
[0143] A 1-L three-necked flask equipped with a thermometer and a
stirring impeller was set in a water bath. The flask was charged
with 875 mL of ion exchanged water at a temperature of
approximately 30.degree. C. and 75 mL of a cationic surfactant
("Texnol (registered Japanese trademark) R5" manufactured by NIPPON
NYUKAZAI CO., LTD., component: alkyl benzyl dimethyl ammonium
salt). Next, the internal temperature of the flask was increased to
80.degree. C. using the water bath. Subsequently, two liquids (a
first liquid and a second liquid) were each dripped into the flask
contents at a temperature of 80.degree. C. over five hours. The
first liquid was a liquid mixture of 12 mL of styrene, 4 mL of
2-hydroxybutyl methacrylate, and 4 mL of ethyl acrylate. The second
liquid was a solution of 30 mL of ion exchanged water in which 0.5
g of potassium peroxodisulfate was dissolved. Then, the flask
contents were polymerized in a state in which the internal
temperature of the flask was kept at 80.degree. C. for two hours.
As a result, a suspension A-1 of resin particulates was
yielded.
[0144] (Preparation of Suspension A-2)
[0145] A suspension A-2 was prepared according to the same method
as for the suspension A-1 in all aspects other than that additive
amounts of the materials were changed. Specifically: the additive
amount of styrene was changed from 12 mL to 13 mL; the additive
amount of 2-hydroxybutyl methacrylate was changed from 4 mL to 5
mL; and the additive amount of ethyl acrylate was changed from 4 mL
to 3 mL.
[0146] (Preparation of Suspension A-3)
[0147] A suspension A-3 was prepared according to the same method
as for the suspension A-1 in all aspects other than that the amount
of the cationic surfactant ("Texnol (registered Japanese trademark)
R5") was changed from 75 mL to 70 mL and the first liquid was
changed from the liquid mixture of 12 mL of styrene, 4 mL of
2-hydroxybutyl methacrylate, and 4 mL of ethyl acrylate to a liquid
mixture of 13 mL of styrene, 6 mL of 2-hydroxyethyl methacrylate,
and 2 mL of methyl acrylate.
[0148] (Preparation of Suspension A-4)
[0149] A suspension A-4 was prepared according to the same method
as for the suspension A-1 in all aspects other than that the amount
of the cationic surfactant ("Texnol (registered Japanese trademark)
R5") was changed from 75 mL to 70 mL and the first liquid was
changed from the liquid mixture of 12 mL of styrene, 4 mL of
2-hydroxybutyl methacrylate, and 4 mL of ethyl acrylate to a liquid
mixture of 12 mL of styrene, 2 mL of 2-hydroxybutyl methacrylate,
and 4 mL of butyl acrylate.
[0150] (Preparation of Suspension A-5)
[0151] A suspension A-5 was prepared according to the same method
as for the suspension A-1 in all aspects other than the followings.
The amount of the cationic surfactant (Texnol (registered Japanese
trademark) R5) was changed from 75 mL to 70 mL, and the first
liquid was changed from the liquid mixture of 12 mL of styrene, 4
mL of 2-hydroxybutyl methacrylate, and 4 mL of ethyl acrylate to a
liquid mixture of 12 mL of styrene, 7 mL of 2-hydroxyethyl
methacrylate, and 2 mL of methyl acrylate.
[0152] (Preparation of Suspension B-1)
[0153] A 3-L flask equipped with a thermometer (thermocouple), a
nitrogen inlet tube, a stirrer, and a heat exchanger (condenser)
was charged with 1,000 g of ion exchanged water at a temperature of
approximately 30.degree. C. and 4 g of a cationic surfactant
("Texnol (registered Japanese trademark) R5" manufactured by NIPPON
NYUKAZAI CO., LTD., component: alkyl benzyl dimethyl ammonium
salt). Subsequently, nitrogen was introduced into the flask
contents for nitrogen substitution for 30 minutes while the flask
contents were stirred. Then, 2 g of potassium peroxodisulfate was
added to the flask. The flask contents were then stirred for
dissolving the potassium peroxodisulfate. While nitrogen was
introduced into the flask, the internal temperature of the flask
was increased to 80.degree. C. A liquid mixture of 250 g of methyl
methacrylate and 4 g of 1,4-butanediol dimethacrylate was dripped
into the flask over two hours starting from the time when the
internal temperature of the flask reached 80.degree. C. During the
dripping of the liquid mixture, the flask contents were kept
stirred under conditions of a temperature of 80.degree. C. and a
rotational speed of 300 rpm. After the dripping, the flask contents
were polymerized in a state in which the internal temperature of
the flask was kept at 80.degree. C. for eight hours. As a result, a
suspension B-1 of resin particulates (specifically, particles of an
acrylic acid-based resin crosslinked by 1,4-butanediol
dimethacrylate) was yielded.
[0154] (Preparation of Suspension B-2).
[0155] A suspension B-2 was prepared according to the same method
as for the suspension B-1 in all aspects other than that a liquid
mixture of 250 g of methyl methacrylate and 4 g of ethylene glycol
dimethacrylate was used instead of the liquid mixture of 250 g of
methyl methacrylate and 4 g of 1,4-butanediol dimethacrylic
acid.
[0156] (Preparation of Suspension B-3)
[0157] A suspension B-3 was prepared according to the same method
as for the suspension B-2 in all aspects other than that the amount
of ethylene glycol dimethacrylate was changed from 4 g to 5 g.
[0158] (Preparation of Suspension B-4)
[0159] A suspension B-4 was prepared according to the same method
as for the suspension B-2 in all aspects other than that the amount
of potassium peroxodisulfate was changed from 2 g to 1 g and the
amount of methyl methacrylate was changed from 250 g to 275 g.
[0160] (Preparation of Suspension B-5)
[0161] A suspension B-5 was prepared according to the same method
as for the suspension B-2 in all aspects other than that the amount
of methyl methacrylate was changed from 250 g to 295 g and the
amount of ethylene glycol dimethacrylate was changed from 4 g to 5
g.
[0162] (Preparation of Suspension B-6)
[0163] A suspension B-6 was prepared according to the same method
as for the suspension B-1 in all aspects other than that the amount
of 1,4-butanediol dimethacrylic acid was changed from 4 g to 3
g.
[0164] The resin particulates contained in the respective
suspensions A-1 to A-5 and B-1 to B-6 had number average particle
diameters and glass transition points (Tg) indicated in Table 2.
For example, the resin particulates contained in the suspension A-1
had a number average particle diameter of 53 nm and a glass
transition point (Tg) of 68.degree. C. The suspensions A-1 to A-5
each were a dispersion of a non-crosslinked resin. The suspensions
B-1 to B-6 each were a dispersion of a crosslinked resin.
[0165] (Preparation of Toner Cores)
[0166] An FM mixer ("FM-20B" manufactured by Nippon Coke &
Engineering Co., Ltd.) was used to mix 100 g of a first binder
resin (crystalline polyester resin synthesized according to the
aforementioned process), 300 g of a second binder resin
(non-crystalline polyester resin A synthesized according to the
aforementioned process), 100 g of a third binder resin
(non-crystalline polyester resin B synthesized according to the
aforementioned process), 600 g of a fourth binder resin
(non-crystalline polyester resin C synthesized according to the
aforementioned method), 144 g of a colorant ("Colortex (registered
Japanese trademark) Blue B1021" manufactured by SANYO COLOR WORKS,
Ltd., component: Phthalocyanine Blue), 12 g of a first releasing
agent ("Carnauba wax No. 1" manufactured by S. Kato & Co.,
component: carnauba wax), and 48 g of a second releasing agent
("NISSAN ELECTROL (registered Japanese trademark) WEP-3"
manufactured by NOF Corporation, component: ester wax) at a
rotational speed of 2,400 rpm.
[0167] The resultant mixture was melt-knead using a twin screw
extruder ("PCM-30" manufactured by Ikegai Corp.) under conditions
of a material feeding speed of 5 kg/hour, a shaft rotational speed
of 160 rpm, and a set temperature (cylinder temperature) of
100.degree. C. The resultant melt-knead product was subsequently
cooled. The cooled melt-kneaded product was then coarsely
pulverized using a pulverizer ("Rotoplex (registered Japanese
trademark)" manufactured by Hosokawa Micron Corporation).
Subsequently, the resultant coarsely pulverized product was finely
pulverized using a jet mill ("Model-I Super Sonic Jet Mill"
manufactured by Nippon Pneumatic Mfg. Co., Ltd.). The resultant
finely pulverized product was classified using a classifier ("Elbow
Jet EJ-LABO" manufactured by Nittetsu Mining Co., Ltd.). As a
result, toner cores were produced that had a Tg of 36.degree. C.
and a volume median diameter (D.sub.50) of 6 .mu.m.
[0168] (Formation of Shell Layer)
[0169] A 1-L three-necked flask equipped with a thermometer and a
stirring impeller was set in a water bath and charged with 300 mL
of ion exchanged water. Thereafter, the internal temperature of the
flask was kept at 30.degree. C. using the water bath. The pH of the
flask contents was then adjusted to pH 4 through addition of dilute
hydrochloric acid to the flask. A first shell material (each
dispersion indicated in Table 1) was then added to the flask. In
manufacture of for example the toner T-1, 15 mL of the suspension
A-1 was added to the flask as the first shell material.
Subsequently, 300 g of the toner cores (toner cores prepared
according to the aforementioned process) were added to the flask
and the resultant flask contents were stirred for one hour at a
rotational speed of 300 rpm. Thereafter, 300 mL of ion exchanged
water was added to the flask.
[0170] The internal temperature of the flask was increased to
78.degree. C. at a rate of 1.degree. C./min. while the flask
contents were stirred at a rotational speed of 100 rpm. A second
shell material (each dispersion indicated in Table 1) was added to
the flask when the internal temperature of the flask reached
78.degree. C. In manufacture of for example the toner T-1, 20 mL of
the suspension B-3 was added to the flask as the second shell
material. The flask contents were then stirred for one hour under
conditions of a temperature of 78.degree. C. and a rotational speed
of 100 rpm.
[0171] The pH of the flask contents was then adjusted to pH 7
through addition of sodium hydroxide to the flask. Subsequently,
the flask contents were cooled to normal temperature (approximately
25.degree. C.), thereby yielding a toner mother particle-containing
dispersion.
[0172] (Washing)
[0173] Filtration (solid-liquid separation) of the toner mother
particle-containing dispersion yielded as above was performed using
a Buchner funnel, thereby collecting a wet cake of the toner mother
particles. The toner mother particles in the resultant wet cake
were re-dispersed in ion exchanged water. Dispersion and filtration
were further repeated five times in order to wash the toner mother
particles.
[0174] (Drying)
[0175] Next, the resultant toner mother particles were dispersed in
an aqueous ethanol solution having a concentration of 50% by mass.
The dispersion of the toner mother particles yielded a slurry of
the toner mother particles. Subsequently, the toner mother
particles in the slurry were dried using a continuous
surface-modifying apparatus ("Coatmizer (registered Japanese
trademark)" manufactured by Freund Corporation) under conditions of
a hot air temperature of 45.degree. C. and flow rate of 2
m.sup.3/min. As a result, a powder of toner mother particles was
obtained.
[0176] (External Addition)
[0177] An FM mixer ("FM-10B" manufactured by Nippon Coke &
Engineering Co., Ltd.) was used to mix 100 parts by mass of the
toner mother particles, 1 part by mass of dry silica particles
("AEROSIL (registered Japanese trademark) REA90" manufactured by
Nippon Aerosil Co., Ltd., content: dry silica particles to which
positive chargeability was imparted through surface treatment,
number average primary particle diameter: 20 nm), and 0.5 parts by
mass of conductive titanium oxide particles ("EC-100" manufactured
by Titan Kogyo, Ltd., matrix: TiO.sub.2 particles, coat layer:
Sb-doped SnO.sub.2 film, number average primary particle diameter:
about 0.35 .mu.m) for five minutes. Through the above process, an
external additive was attached to the surfaces of the toner mother
particles. Thereafter, the resultant powder was sifted using a 200
mesh sieve (opening: 75 .mu.m). As a result, a toner (each toner
T-1 to T-15 indicated in Table 1) containing multiple toner
particles was produced.
[0178] [Evaluation Methods]
[0179] Each sample (toners T-1 to T-15) was evaluated according to
the following evaluation methods.
[0180] (Lowest Fixing Temperature)
[0181] A ball mill was used to mix 100 parts by mass of a developer
carrier (carrier for "TASKalfa5550ci" manufactured by KYOCERA
Document Solutions Inc.) and 10 parts by mass of a sample (toner)
for 30 minutes, thereby preparing a two-component developer.
[0182] The lowest fixing temperature of the toner was evaluated
through formation of an image using the two-component developer
prepared as above. An evaluation apparatus used was a color printer
including a heat and pressure applying fixing device of
roller-roller type ("FS-C5250DN" manufactured by KYOCERA Document
Solutions Inc. that was modified as an evaluation apparatus so that
the fixing temperature was variable). The two-component developer
prepared as above was loaded into a developing device of the
evaluation apparatus, and the sample (toner for replenishment use)
was loaded into a toner container of the evaluation apparatus.
[0183] A solid image (specifically, an unfixed toner image) having
a size of 25 mm.times.25 mm was formed on paper of 90 g/m.sup.2
(A4-size printing paper) using the above evaluation apparatus in an
environment of a temperature of 23.degree. C. and a humidity of 60%
RH under conditions of a linear velocity of 200 mm/sec. and a toner
carrying amount of 1.0 mg/cm.sup.2. Subsequently, the paper on
which the image has been formed was allowed to pass through the
fixing device of the evaluation apparatus.
[0184] A fixing temperature set in evaluation of the lowest fixing
temperature ranged from at least 100.degree. C. to no greater than
200.degree. C. Specifically, a lowest temperature (lowest fixing
temperature) at which a solid image (toner image) was fixable was
measured while the fixing temperature of the fixing device was
increased 5.degree. C. by 5.degree. C. (2.degree. C. by 2.degree.
C. around the lowest fixing temperature) gradually starting from
100.degree. C. Whether or not toner fixing was accomplished was
checked by a fold-rubbing test as described below. Specifically,
the fold-rubbing test was performed by folding the paper in half
such that a surface on which the image was formed was folded
inwards, and by rubbing a 1-kg weight covered with cloth back and
forth on the fold five times. Next, the paper was opened up and a
fold portion (i.e., a portion of the paper on which the solid image
was fixed) was observed. The length of toner peeling of the fold
portion (peeling length) was measured. The lowest temperature among
temperatures for which the peeling length was no greater than 1 mm
was determined to be a minimum fixing temperature. A toner having a
lowest fixing temperature of no greater than 145.degree. C. was
evaluated as good. A toner having a lowest fixing temperature of
greater than 145.degree. C. was evaluated as poor.
[0185] (High-Temperature Preservability)
[0186] A 20-mL polyethylene vessel was charged with 2 g of a sample
(toner), sealed, and left to stand for three hours in a constant
temperature bath set at a temperature of 58.degree. C. The toner
taken out from the constant temperature bath was then cooled to
room temperature, thereby obtaining an evaluation toner.
[0187] The resultant evaluation toner was placed on a 100-mesh
sieve (opening: 150 .mu.m) having a known mass. The mass of the
toner prior to sifting was then calculated by measuring the total
mass of the sieve and the evaluation toner thereon. Next, the sieve
was placed in a powder tester (product of Hosokawa Micron
Corporation) and the evaluation toner was sifted in accordance with
a manual of the powder tester by shaking the sieve for 30 seconds
at a rheostat level of 5. The mass of toner remaining on the sieve
was calculated by measuring the total mass of the sieve and toner
thereon after the sifting. An aggregation rate (unit: % by mass)
was calculated from the mass of the toner prior to sifting and the
mass of toner after sifting (mass of toner remaining on the sieve
after sifting) based on the following equation.
Agglomeration rate=100.times.(mass of toner after sifting)/(mass of
toner before sifting).
[0188] The toner having an agglomeration rate of no greater than
50% by mass was evaluated as good. The toner having an
agglomeration rate of greater than 50% by mass was evaluated as
poor.
[0189] [Evaluation Results]
[0190] Table 3 indicates results of evaluation of high-temperature
preservability (aggregation rate) and low-temperature fixability
(lowest fixing temperature) for the samples (toners T-1 to
T-15).
TABLE-US-00003 TABLE 3 High-temperature Low-temperature
preservability fixability Toner [% by mass] [.degree. C.] Example 1
T-1 21 130 Example 2 T-2 16 134 Example 3 T-3 15 142 Example 4 T-4
17 134 Example 5 T-5 34 126 Example 6 T-6 5 136 Example 7 T-7 48
138 Example 8 T-8 48 140 Comparative Example 1 T-9 68 (poor) 122
Comparative Example 2 T-10 59 (poor) 136 Comparative Example 3 T-11
62 (poor) 130 Comparative Example 4 T-12 55 (poor) 126 Comparative
Example 5 T-13 7 150 (poor) Comparative Example 6 T-14 8 146 (poor)
Comparative Example 7 T-15 64 (poor) 124
[0191] The toners T-1 to T-8 (toners according to Examples 1-8)
each have the above basic structure. Specifically, the shell layers
of the respective toners of Examples 1-8 each had a film-shaped
first domain and particle-shaped second domains. The first domain
was formed substantially from a non-crosslinked resin, while the
second domains were formed substantially from a crosslinked resin
(see Tables 1 and 2). The crosslinked resin had a glass transition
point (Tg) 45.degree. C. or more greater than the non-crosslinked
resin. In the toner T-1, for example, the non-crosslinked resin had
a Tg of 68.degree. C. (see Table 2) while the crosslinked resin had
a Tg of 130.degree. C. (see Table 2). A Tg difference (=(Tg of
crosslinked resin)-(Tg of non-crosslinked resin) was 62.degree. C.
(see Table 1). Furthermore, the first domain had an average height
(first shell thickness) from the surfaces of the toner cores of at
least 10 nm and less than 50 nm. Yet, the second domains had an
average height (second shell thickness) from the surfaces of the
toner cores of at least 50 nm and no greater than 100 nm. For
example, the toner T-1 had a first shell thickness of 16 nm (see
Table 1) and a second shell thickness of 79 nm (see Table 1). The
toners according to Examples 1-8 each were excellent in both
high-temperature preservability and low-temperature fixability, as
indicated in Table 3. Note that the shell layers in each of the
toners T-1 to T-8 (toners according to Examples 1-8) contained the
cationic surfactant. Specifically, the cationic surfactant (alkyl
benzyl dimethyl ammonium salt) used in preparation of the shell
material (suspension) was attached to the respective surfaces of
the first and second domains. Furthermore, the area of the second
region was larger than that of the third region. The second
coverage was at least 70% and no greater than 99%. A ratio (second
coverage) of the total length of regions covered with at least one
of film-shaped domains and particle-shaped domains relative to the
surface region (a contour line indicating an outer circumference)
of the toner core was measured on a taken TEM image (a sectional
image of the toner particle). Specifically, the second coverage was
calculated based on an equation "second coverage=100.times.(total
length of regions covered with at least one of film-shaped domains
and particle-shaped domains)/(circumferential length of toner
core)".
* * * * *